Umbrella



FIG. 1 is a perspective view of an umbrella showing my present design;

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a left view thereof;

FIG. 5 is a right view thereof;

FIG. 6 is a top plan view thereof; and,

FIG. 7 is a bottom plan view. 

The ornamental design for an umbrella, as shown and described. 